Broach tools have been used for many years for the machining of metal, and for specific operations such as broaching slots, openings or channels of specialized cross-section. The conventional broaching tool has been a unitary broach having a plurality of cutting teeth formed on a single solid elongated member. Several shortcomings however, have been associated with the use of such elongated broaches. For example, the quality of the overall tool is only as good as the worst tooth, with the existence of an undersized tooth resulting in an overloading of the next tooth, as well as making it necessary, through wear or otherwise, to discard the entire tool even though there is still useful life left in many or all of the other teeth. Of course, the entire tool is also lost as the result of any tool damage or cracking with respect to any one tooth or any one part of the tooth. In addition, the type of material from which the tool is made is restricted. More particularly, while high speed steels have been used to form the elongated broaches, tougher, more expensive materials such as carbides, cannot be used because of the prohibitive costs associated with the initial manufacture of the tool, as well as the cost of replacements necessitated by the fact that damage to any one part of the tool requires it to be discarded.
Another type of broaching tool which has been used is one which includes a plurality of separate cutting inserts which are fixed to the tool body. Typically, the inserts are formed from a cemented carbide or other hard metal. The conventional design for tools of this type are generally of brazed construction, i.e. carbide blanks are permanently fastened to a steel holder with brazed material and ground after brazing to the required cutter configuration. Proper brazing of the carbide to the steel along with grinding the carbide after brazing is critical, yet due to space limitations, is extremely difficult. The brazing of the carbide tips requires that each be held in proper position during the brazing procedure to facilitate grinding to form after brazing. Furthermore, it is necessary for a successful broaching operation that each tip is securely and properly brazed to the steel body. Unfortunately, it is often common for a brazed joint to come apart in the grinding operation or in the actual broaching of the part. In either event, if the carbide tip breaks, a new tip must be rebrazed and the form reground. The conventional brazed construction thus offers little advantage over high speed tooling since downtime and requalifying of a broach set is a lengthy process. In addition to broaches having brazed inserts, there are tools in which the cutting inserts are in some way clamped to the tool.
Overall, broaching is an excellent method of machining many materials when both precision and high production rates are required. In particular, it is widely used in the automotive industry for forming various contours into engine blocks and other automotive components. While the rate of production of broaches is high, this has been somewhat offset in the past by the relatively high cost of the initial broach and of resharpening the broach after it has become dulled. To overcome the later of these difficulties, various designs using indexable and reversible inserts have been introduced. However, not all of these designs have been capable of producing cuts that were as precise or economical as could be desired. In particular, some of these designs resulted in uneven chip load upon the inserts which is thought to cause precision lessening vibration. In addition, uneven chip load also results in inserts wearing at varying rates so that either all inserts are indexed at one time even, if only some are worn; or when production is stopped for indexing or replacement, the worn inserts are indexed or replaced, but production is halted again later when other inserts become worn. Either procedure is less than ideal. A further detriment to some of these designs is found in the uneven power requirements resulting from rows of inserts entering the workpiece simultaneously. Thus, with those designs presenting rows of inserts, the power required would increase suddenly each time a row of inserts contacted the workpiece then decrease suddenly each time a row left the workpiece. It is thought that in some cases, this might have contributed to vibration and hence, harmed precision of the machining operation.